There are many applications where accurate measurement of pressure requires the use of miniaturized pressure sensors, including monitoring of physiological parameters, process monitoring of industrial facilities and automobile performance monitoring. In medical applications, miniaturized sensors are used for both invasive and non-invasive measurement of blood pressure as well as measurement of other body pressures for diagnostic purposes. In many instances, improved monitoring of the parameters of interest requires the use of closely spaced sensing devices. Blood pressure measurement by tonometry, for example, requires pressure sensors narrower than the underlying artery and is facilitated by sensor element spacing smaller than the artery width.
Many of the pressure sensors employed for medical monitoring are based on strain gage or capacitance measurement techniques. U.S. Pat. No. 4,881,410, for example, discloses a silicon pressure sensor based on capacitance measurement which requires fabricating a sophisticated structure of metal and silicon on the surface of a chip. The pressure sensitivity of the device is controlled by scaling the dimensions of the sensor. U.S. Pat. No. 4,771,638 discloses a pressure sensor operating on the strain gage principle. Sensors such as those described above are generally built in layers parallel to the underlying substrate of the micro chip. The large surface areas needed by these conventional sensors to produce signals large enough for accurate measurement limits the density of pressure sensing devices on the chip surface.
Although field emitter arrays have been used in semiconductor devices, e.g., U.S. Pat. Nos. 4,721,885 and 4,835,438, and have also been used as electron sources in semiconductor and cathode ray tube (CRT) displays, e.g., U.S. Pat. No. 4,766,340, heretofore pressure sensors have not been produced using such a technique or incorporating such a device.